Levothyroxine

Administration

• Type: Endocrine, synthetic hormone
• Dosage Forms: Tablet 13mcg, 25mcg, 50mcg, 75mcg, 88mcg, 100mcg, 112mcg, 125mcg, 137mcg, 150mcg, 175mcg, 200mcg. IV 100mcg, 200mcg, 500mcg
• Routes of Administration: PO, IV
• Common Trade Names: Synthroid

Adult Dosing

• Myxedema coma: 300-500 mcg IV x1, then 50-100mcg IV daily until able to tolerate PO
• Hypothyroidism: doses vary

Pediatric Dosing

• Hypothyroid: Doses vary, 1.7-15 mcg/kg/day PO

Special Populations

• Pregnancy Rating: A
• Lactation risk: Infant risk minimal
• Renal dosing: Not defined
• Hepatic dosing: Not defined

Contraindications

• Allergy to class/drug, hypersensitivity to glycerol
• Uncorrected adrenal insufficiency (may precipitate acute adrenal crisis)
• Acute MI
• Subclinical or overt thyrotoxicosis, nontoxic diffuse goiter, nodular thyroid disease

Adverse Reactions

Serious

• MI, heart failure, tachycardia, cardiac arrest
• Pseudotumor, seizure
• Dyspnea
• Hyperthyroid
• Decreased bone mineral density, hip fracture

Common

• Palpitations
• Diarrhea
• Anxiety, insomnia, fatigue, sweating, weight loss
• Alopecia

Pharmacology

• Half-life: 6-7 days
• Metabolism: Hepatic
• Excretion: Renal, fecal

Mechanism of Action

• Synthetic thyroid hormone (T4)

See Also

• Hypothyroidism, Myxedema coma